Methods and Mobile Routers in a Communications System for Routing a Data Packet

ABSTRACT

The present invention relates to moving networks in communication systems. An object of the invention is to provide moving network nodes ( 205, 206 ) in a moving network ( 201 ) with the ability to simultaneously access several external access networks ( 211, 212, 213 ) accessible by different mobile routers ( 204, 207 ) such that a data packet directed to an address external to the moving network can be sent from a moving network node via any of the mobile routers ( 204, 207 ) and via a tunnel setup in any of the simultaneously accessible external accesses to a home agent ( 216 ) in a home network ( 215 ) of the mobile router. This is achieved by synchronizing between the mobile routers data regarding the external accesses of each mobile router, and, when a data packet is received at a first mobile router ( 204 ), the first mobile router selects external access based on the synchronized external access information, information in the data packet and optionally also based on access selection policies. If a selected access belongs to e.g. a second mobile router ( 207 ), the packet is forwarded from the first mobile router to the second mobile router before it is sent to the home agent ( 215 ) via the tunnel setup through the selected access ( 211 ).

FIELD OF THE INVENTION

The present invention relates to mobile routers and methods in acommunication system for routing a data packet, and more particularly itrelates to methods and mobile routers for routing a data packet from amoving network to a home network.

BACKGROUND OF THE INVENTION

In communication systems based on packet data communication, for examplebased on the Internet Protocol (IP), there is a need for a mobilecommunication node to be able to communicate with a fixed networkinfrastructure even when the mobile communication node moves such thatit changes its point of attachment to the fixed network infrastructure:The mobile communication node could for example move such that it needsto change from communicating with a first access point belonging to afirst Wireless Local Area Network (WLAN) to communicating with a secondaccess point belonging to a second WLAN.

Mobile IPv6 and Mobile IPv4 are prior art protocols enabling suchmobility in IPv6 based and IPv4 based networks, respectively. MobileIPv6 is described e.g. in the document “Mobility Support in IPv6” by D.Johnson et al, RFC3775, published on the Internet by the Network WorkingGroup of the Internet Engineering Task Force in June 2004. FIG. 1 showsa Mobile IPv6 based system and below is explained how mobility isachieved for a mobile communication node in such a Mobile IPv6 basedsystem. The mobile communication node 105, which could be anycommunication device, for example a laptop or a mobile phone, has a homenetwork 110, which has a Home Agent 111 and a Router 112. The mobilecommunication node has a stable home address belonging to the addressspace of the home network. FIG. 1 also shows a first foreign network 120having at least one Access Point 121 and an access router 122, and asecond foreign network 130 comprising an access router 132 and acorrespondent node 135 connected to the Access Router 132. All networksare connected via an IP network 140, e.g. the Internet. In a scenario,the mobile communication node 105 is in its home network 110 and hasestablished a connection to the correspondent node 135 connected to thesecond foreign network 130. The mobile communication node then movesfrom the home network to the first foreign network 120. The mobilecommunication node will then, according to Mobile IPv6, send a BindingUpdate (BU) message (which corresponds to a Registration Request inMobile IPv4) via the first foreign network to the Home Agent 111 of thehome network 110 informing the Home Agent of the mobile node's newaddress, i.e. it's care-of address in the first foreign network.Thereafter, the Home Agent 111 sends a Binding Acknowledge message(which corresponds to a Registration Reply in Mobile IPv4) to the mobilecommunication node and a tunnel is established between the mobilecommunication node and the Home Agent, via the IP network 140. On themobile communication node endpoint the tunnel has the mobilecommunication node's care-of address as its outer address and the mobilecommunication node's home address as its inner address. The followingtraffic from the mobile communication node to the correspondent node 135will then transit through the tunnel to the Home network and further tothe correspondent node in the foreign network such that the previousconnection between the mobile communication node and the correspondentnode is preserved. Packets in the other direction, originating from thecorrespondent node 135, are addressed to the home address of the mobilecommunication node 105, intercepted by the Home Agent 111 and forwardedthrough the tunnel to the mobile communication node 105.

In another scenario not just a mobile communication node may be movablein relation to its home network, but a whole network, for example anetwork within a transport vehicle (e.g. bus, train or airplane). Inthis case, this so called moving network will have a router throughwhich all communication nodes in the moving network can communicate. Inthe case of a moving network on e.g. an airplane, the moving networkwill comprise communication nodes, which may be different users'communication devices, such as laptops, mobile phones, PDAs (PersonalDigital Assistants) etc., which communication nodes communicate wirelessor wireline with a router within the airplane, such that allcommunication destined to an external address will pass via the router.A moving network may also be e.g. a Personal Area Network (PAN), whereina PAN comprises all communication devices belonging to a user andsituated within short range radio communication distance form eachother, see for example co-pending patent application PCT/SE2004/001027.In this case, the communication devices in the PAN, called PAN devices,will communicate via a PAN device that has external accesspossibilities, e.g. a mobile phone having access to a GPRS network, suchthat the PAN device having external access possibilities works like arouter for data originating from any PAN device and being directed to anaddress external of the PAN.

This document deals with mobility for a moving network, which is definedas a network that is mobile in relation to its home network. A movingnetwork can change its point of attachment to a fixed infrastructure orit may have many points of attachment to a fixed infrastructure, but itis still able to communicate with its home network. A moving network isalso characterized in that the nodes generating traffic are situated inthe network. Such node in a moving network is called a moving networknode. In this document, each node in the moving network or connected tothe moving network that works like a router for data originating from amoving network node is defined as a mobile router. Examples of suchmobile routers are: a PAN device working as a router in a PAN, and arouter in a moving network on a vehicle. Note that a node may have bothroles, i.e. being both a moving network node and a mobile router, forexample a PAN device such as a mobile phone in a PAN.

“The Network Mobility (NEMO) Basic Support Protocol”, by Devarapalli etal, published June 2004 as an Internet Draft, which is a workingdocument of the Internet Engineering Task Force, is a protocol thatenables a moving network to attach to different points in the Internet.The protocol is an extension of Mobile IPv6 and allows sessioncontinuity for every communication node (or communication device) in themoving network as the network moves. It allows a mobile router tomaintain a stable network prefix for a moving network, even as themobile router changes its, and thus the moving network's, point ofattachment to a fixed network infrastructure. This prefix stability isachieved through a solution similar to the mobile IPv6 solution, i.e. bymaking a home agent (HA) in the home network of the mobile router afixed point of attachment for the Mobile Router (MR) and maintainingconnectivity between the HA and the MR through a tunnel. The prefix isallocated from the address range of the home network, and can thusremain the same even as the MR and its network move. When the MRattaches to a network in a new location, it acquires a new care-ofaddress, but its home address and prefix are unchanged. However, justlike in Mobile IPv6 the MR has to register its new care-of address inthe HA in order to maintain the tunnel between the Mobile Router and theHome Agent.

If, in the current NEMO solution, a bad tunnel is experienced, it willbe replaced by a new tunnel by performing a new registration with theHA, this time with a different care-of address, unless the tunnel isre-established through the same interface and point of attachment, andpossibly configured on a different interface, depending on the nature ofthe tunnel problems. If a communication node could get Internet accessthrough multiple access media simultaneously, i.e. could have multipletunnels established simultaneously, a data flow could be moved from abad tunnel to a good tunnel much quicker than if only one tunnel at atime can be established. Also, for matters of cost, bandwidth, delayetc. it could be useful for a communication node to get Internet accessthrough multiple simultaneous tunnels. However, the NEMO basic supportprotocol does not allow this because it allows only a single care-ofaddress to be registered in the Home Agent (HA) for a certain MobileRouter (MR) at any one time. Multiple simultaneous care-of addresses arenot allowed and thus multiple simultaneous accesses and MR-HA tunnelsare not possible for a MR.

In the co-pending patent application PCT/SE2004/001578 by the sameapplicant, a procedure is suggested for managing different externalaccess resources simultaneously accessible by a mobile router in amoving network, such that a network according to FIG. 2 based on amobile IP-like solution can be established. In FIG. 2, which shows amoving network 201 situated e.g. on a train 200, a mobile router 204 ofthe moving network 201 has a home agent 216 in his home network 215 anda home address and one or more prefixes out of the address range of thehome network 215. Moving network nodes 205, 206 attach to the movingnetwork via access points 202, 203 such that they can communicate withthe rest of the nodes in the moving network. When the moving networkmoves, the mobile router 204 may attach to a foreign network. In thiscase, a tunnel will be set up between the mobile router over the foreignnetwork to the Home Agent 216 in the home network. In this way,according to mobile IP, the mobile router will get a care-of-address toits new location such that it can be reached by a correspondent node viaits original address in the home network. In the network shown in FIG.2, three tunnels are established simultaneously over three foreignnetworks and an IP network 214 between the Home Agent and the mobilerouter such that the mobile router has ability to access three differentforeign networks 211, 212, 213. To the moving network this ability toaccess three different foreign networks can be seen as an ability to usethree different external access resources: a WCDMA network 213, asatellite access network 212 and a GPRS network 211. To be able to fullymake use of the three different external access resources, thisprocedure suggests that the mobile router controls the use of thedifferent external access resources both for data packets sent in thedirection to the home agent and for data packets sent from the homeagent to the mobile router. To achieve this, the mobile router 204classifies a data packet received from a moving network node 205, 206based on information in the packet and selects an access resource forsending the packet based on the classification. The mobile router alsosends implicit or explicit information to the home agent regardingrouting of data packets from the home agent to the mobile router, suchthat the home agent classifies these data packets and selects accessresource for sending the data packets based on the information receivedfrom the mobile router. With this procedure, a moving network node hasthe ability to use any of the external accesses of the mobile routersimultaneously, such that it can quickly change access e.g. if oneexternal access goes down. Since all decisions regarding which externalaccess to use lies with the mobile router, the moving network nodes donot have to bother about the selection process and, consequently, do nothave to have any extra functionality for selecting access.

The procedure described above only discusses a moving network having onemobile router with a plurality of external access possibilities.Although, it may happen that all external accesses present in an areaare not handled by one and the same mobile router. For example, on atrain there may be a fixed mobile router mounted in eachrailway-carriage. Also, for technical reasons, different externalaccesses may not be handled by the same mobile router. Therefore, to beable to give the moving network nodes in a moving network the ability touse all external accesses that are present in an area, there is a needfor a function that can provide a moving network node with the abilityto access external accesses provided by different mobile routers in amoving network such that a data packet can be sent from a moving networknode and directed to an address external to the moving network via anyof a number of external accesses provided by the different mobilerouters. Also, there is a need to control the use of the differentexternal accesses provided by the different mobile routers such that theexternal accesses are used in an efficient way.

The term flow or data flow used in the application is a loose term for aconnection between two end nodes. A flow between a first and a secondend node may have two directions: from the first node to the second nodeand vice versa. Thus, in the application, a data flow comprises anuplink part and a downlink part, wherein the uplink part is in thedirection from the moving network node to the home agent (and further tothe correspondent node), and the downlink part is in the direction fromthe home agent to the moving network node. A TCP (Transmission ControlProtocol) connection is typically seen as a flow. A node can havemultiple flows towards different correspondent nodes and also multipleflows towards the same correspondent node. Each flow comprises datapackets. A flow is typically defined by the source and destination IPaddresses and port numbers, plus the transport protocol in use, such asTCP or UDP (User Datagram Protocol). It is also possible to insteaddefine a flow by its flow label (in IPv6) or its SPI (Security ParameterIndex) together with the source and destination IP addresses, and theprotocol in case of the SPI. The flow label is more specific than theport numbers and should have precedence over them. The SPI is used inIPsec (IP security as defined in RFC 2401 “Security Architecture for theInternet Protocol”), together with the destination IP address and theprotocol to identify the security association, and the SPI-destinationaddress-protocol triplet is typically used as a (unidirectional) flowidentifier when the packet is encrypted and the port numbers are visibleonly to the receiving end-node. The terms link, access and externalaccess used in the application are synonymous. One external access orlink defines one possible way of getting external access from the movingnetwork. There is one tunnel established between a Mobile Router and aHome Agent per external access.

The term Home Agent used in the application should be interpreted as anynode in a home network working like a mobile anchor point to the movingnetwork, i.e. facilitating communication from the moving network over anexternal network and the home network, such that the present inventioncan be used.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a moving network withthe ability to simultaneously access external accesses provided bydifferent mobile routers of the moving network.

The above object is achieved by a method, a mobile router and a computerprogram product set forth in the characterizing part of the independentclaims.

This is provided by each mobile router having information about theexternal accesses in the moving network, and by, when a first mobilerouter receives a data packet from a moving network node, the firstmobile router selecting over which of all external accesses in themoving network to route the data packet based on information in the datapacket and on the external access information. Thereafter, the packet isrouted over the selected external access.

According to a first aspect of the invention, a method is provided in acommunication system for routing a data packet originating from a movingnetwork node in a moving network via a first mobile router of the movingnetwork to a home agent in a home network of the moving network. Thefirst mobile router has ability to access at least one first externalaccess through which at least one first external access one tunnel eachis set up to a first home agent of the first mobile router. The movingnetwork also has at least one second mobile router which has ability toaccess at least one second external access, through which at least onesecond external access one tunnel each is set up to a second home agentof the at least one second mobile router. Each mobile router in themoving network has information regarding the at least one first and theat least one second external accesses in the moving network. The methodcomprises the steps of:

-   -   receiving, at the first mobile router, a data packet from a        moving network node;    -   selecting, in the first mobile router, one of the at least one        first or second external accesses for routing the data packet to        the first or second home agent based on information in the data        packet and on the information regarding the at least one first        and the at least one second external accesses;    -   routing the data packet from the first mobile router to the        first or second home agent via the tunnel set up through the        selected external access.

According to a second aspect of the invention, a mobile router of amoving network is provided in a communication system, which mobilerouter is arranged for routing a data packet originating from a movingnetwork node in the moving network to a home agent in a home network ofthe moving network. The mobile router has ability to access at least onefirst external access, through which at least one first external accessone tunnel each is set up to a first home agent of the mobile router.The mobile router comprising:

-   -   means for storing information regarding the at least one first        external access and regarding at least one second external        access, which at least one second mobile router has the ability        to access, and through which at least one second external access        one tunnel each is set up to a second home agent of the at least        one second mobile router;    -   means for receiving a data packet from a moving network node;    -   means for selecting one of the at least one first or second        external accesses for routing the data packet to the first or        second home agent, wherein the selection that the means for        selecting is arranged to accomplish is based on information in        the data packet and on the information regarding the at least        one first external access and the at least one second external        access; and    -   means for routing the data packet to the first or second home        agent via the tunnel set up through the selected external        access.

According to a first embodiment of the invention, the selection overwhich external access to route the data packet is also based on externalaccess policies residing in the mobile routers.

According to a second embodiment of the invention, the external accessinformation and the external access policies are synchronized betweenthe mobile routers in the moving network when required, such that themobile routers will make the same routing decision for a data packet.

An advantage with the present invention is that the invention makes itpossible for a moving network node to get access to external accessesavailable from different mobile routers in the moving network.

A further advantage of the present invention is that the routingdecisions made in the mobile routers are transparent to the movingnetwork nodes, meaning that the moving network nodes do not have to beupgraded in any way to be able to access external accesses provided bydifferent mobile routers.

A still further advantage is that the external accesses of the differentmobile routers are simultaneously accessible from the moving network,such that e.g. more bandwidth can be available to the moving networknodes.

Another advantage is that if a mobile router for some reason losescontact with the rest of the moving network, e.g. goes down, the movingnetwork can still get external access via the other mobile routers inthe moving network. Also, since the external accesses are simultaneouslyaccessible, an ongoing session (data flow transmission) can betransferred to another access if an access or a mobile router goes down,such that the ongoing session is not lost.

Yet another advantage of the invention is that it can handle the casewhen there are many different mobile routers at hand in an areasimultaneously without having to upgrade the moving network nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in more detail withreference to enclosed drawings, wherein:

FIG. 1 shows a schematic block diagram of a communication systemaccording to prior art;

FIG. 2 shows a schematic block diagram of another communication systemaccording to prior art;

FIG. 3 illustrates a schematic block diagram of a communication systemwherein the present invention can be used;

FIG. 4 is a flow chart of a method according to an embodiment of theinvention;

FIG. 5 illustrates a schematic block diagram of another communicationsystem wherein the present invention can be used;

FIG. 6 is a schematic block diagram showing the routing of a packetaccording to an embodiment of the invention called a distributedsolution;

FIG. 7 is a schematic block diagram showing the routing of a packetaccording to an embodiment of the invention called a centralizedsolution;

FIG. 8 shows a diagram of the range of possible values used forselecting super mobile router in the centralized solution;

FIG. 9 shows a schematic block diagram of a mobile router according toan embodiment of the invention.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements.

FIG. 3 shows a schematic block diagram of an exemplary communicationsystem wherein the present invention can be used. The system is similarto the prior art FIG. 2, with the difference that the system of FIG. 3has two different mobile routers, a first mobile router 204 and a secondmobile router 207, compared to a single MR in the system of FIG. 2. Thesystem has a Vehicle Area Network (VAN) 201 which is an example of amoving network for which the present invention can be used. The VAN 201is in this case situated on a train 200, which may be moving. The VANmay be some sort of switched Ethernet that may have either Ethernetports 202 or WLAN access points 203 or a combination of Ethernet portsand WLAN access points (as shown in the figure). Moving network nodes(MNNs) 205, 206 may connect to an Ethernet port or to a WLAN accesspoint. The moving network nodes may be any communication node such aslaptops or mobile phones belonging to persons travelling on the train.As mentioned above, the exemplary VAN also has a first and a secondMobile Router (MR) 204, 207 which act as default gateways for the MNNsinside the vehicle, such that a data packet sent from a moving networkand directed to an external network address can be sent via any of themobile routers. The mobile routers 204, 207 are responsible for mobilitymanagement for the entire VAN 201, i.e. mobility management is totallytransparent to the MNNs 205, 206 entering the vehicle. This means thatno new requirements are put on the MNNs when joining the VAN. The firstand the second mobile router have the same home agent 215 in the samehome network and the same address prefix from the address range of thehome network. This facilitates their shared responsibility for themobility management of the moving network according to the invention.Although, it may be possible that the first and the second mobilerouters have different home agents that can reside in the same homenetwork or in different home networks. Of course, it is also possible tohave more than two mobile routers offering external access. For thepurpose of routing packets destined to an external network address, thefirst and the second mobile router 204, 207 have external accesses forthe VAN comprising one or several different access networks. In FIG. 3the first mobile router 204 has two external accesses, a first externalaccess via a Wideband Code Division Multiple Access (WCDMA) network 213and a second external access via a satellite radio communication network212. The second mobile router 207 has one external access via a GeneralPacket Radio Service (GPRS) network 211. Each of these access networksis available via geographically distributed access points belonging toeach access network, as is well known in the art. One or several ofthese access networks can be available at the same time depending on forinstance coverage and operator policies. FIG. 3 also shows a Home Agent(HA) 216 in a home network 215, which in the example is the home networkfor both the first mobile router 204 and the second mobile router 207.Data packets from any of the MNNs and destined for e.g. a correspondentnode in a foreign network is routed via any of the access networks, anIP network 214 and via the home agent 216 in the home network 215. Forthis purpose, a first tunnel is set up from the first mobile router 204over the WCDMA network 213 and the IP network to the home agent 216 inthe home network 215, a second tunnel is set up from the first mobilerouter 204 over the satellite communication network 212 and the IPnetwork to the home agent 216 and a third tunnel is set up from thesecond mobile router 207 over the GPRS network 211 and the IP network tothe home agent. It is also possible that two mobile routers have thesame type of access, e.g. that both MRs have WCDMA access. According tothe invention, the different external accesses offered by the networks211, 212, 213 can be used simultaneously by the moving network, as willbe described later.

There are several reasons motivating why support for simultaneous usageof several accesses would be beneficial in the scenario of FIG. 3:

-   -   It would be possible to handle the dynamic nature of the        external accesses, i.e. the fact that accesses will go up and        down depending on access technology and coverage. By having        multiple simultaneous accesses, the MRs will be able to quickly        move traffic between the different accesses when for instance        one access goes down. According to the invention, moving traffic        can take place both between two accesses of a single MR or        between two accesses of two different MRs.    -   Simultaneous use of multiple external accesses means more        bandwidth to the users of the moving network nodes in the moving        network, which would improve the communication possibilities for        the moving network nodes.    -   Also, to do load-sharing between the different external        accesses, using different load-sharing algorithms, would improve        the performance of the system and the users' system experience.

The solution according to the invention will make it possible for amobile node, e.g. the moving network node 205 in FIG. 3, in the movingnetwork to use any of the available external accesses, even an accessprovided by the second mobile router, despite the fact that the mobilenode has the first mobile router as its default router, i.e. that themobile node sends its packets to the first mobile router. Since therouting decisions are made in the mobile routers, the moving networknodes do not have to be upgraded to be able to access external accessesprovided by different mobile routers.

Also, a mobile node may choose MR arbitrarily. This means that datapackets belonging to the same flow may end up in different mobilerouters. Still, the packets should be sent over the same externalaccess. Therefore, the choice of access is made consistently across allMRs in the moving network. For this case, the MRs according to thesolution are synchronized such that conditions for choosing externalaccess are the same for all mobile routers such that e.g. packetsbelonging to the same flow are sent over the same access.

In the system described above in relation to FIG. 3, the solution of theinvention achieves that a moving network node can use any of thedifferent external access resources of a moving network even if they areprovided by different MRs. It also achieves that the different externalaccess resources can be used in an efficient way for the moving network.In FIG. 4 an embodiment of a method according to the invention is shownin relation to the system of FIG. 3.

Supposing that the moving network node 205 is about to send a packet toan external node (not shown in FIG. 3). The packet will then be sent viaany of the mobile routers 204, 207, and via a tunnel over any of theaccess networks 211, 212, 213 and over the IP network 214 to the homeagent 216 of the home network 215 of the mobile routers 204, 207, whichhome agent routes the packet further to the external node. The tunnelshave been established by each MR creating a Care of Address (CoA) oneach external access interface such that each CoA has been registeredwith the Home Agent. In an embodiment of the invention it is assumedthat all MRs of the moving network register with the same HA and thatthe MRs all use the same Mobile Network Prefix (MNP). The MNP is theaddress space an MR has been delegated (e.g. from the HA) and that itallows MNNs to form addresses from. However, it is also possible withinthe scope of the invention that different MRs use different MNP, andthat different MRs register with different HAs.

When a packet is sent from a moving network node to any of the MRs, theMRs, e.g. the first and the second mobile router 204, 207 of FIG. 3,have information about each other's external accesses, informationregarding e.g. which external accesses the other mobile routers in themoving network have, which capacity the external accesses have, themomentary status of the external accesses etc. This information has beentransmitted from and received by all MRs of a moving network. Whenrequired, for example when a type of information has changed, thisinformation is exchanged between all the MRs such that all MRs have thesame information regarding the external accesses in the moving network,i.e. the information regarding the external accesses in the movingnetwork is synchronized among the mobile routers in the moving network.A synchronization may also take place on a periodical basis.

According to a preferred embodiment of the method of the invention shownin FIG. 4 and used for the exemplary system according to FIG. 3, when adata packet has been sent 401 from the moving network node 205 to one ofthe mobile routers 204, 207, e.g. the first mobile router 204, the firstmobile router selects 402 one of the different external accessesprovided by the first mobile router or the second mobile router forrouting the data packet to the home agent via one of the tunnels set upover each of the external access networks 211, 212, 213. The selectionis based on information in the data packet and on the information aboutthe external accesses. When required the selection is also based onconfiguration and access selection policies in the MRs. Information inthe data packet used for the selection may for example be a flowidentification such as source and destination IP address plus one of:

-   -   source and destination port number plus protocol number,    -   flow label, or    -   Security Parameter Index (SPI) and protocol number, which in        this case will indicate a security protocol such as        Encapsulating Security Payload (ESP) or Authentication Header        (AH).

Thereafter, if the selected external access is in the first mobilerouter 403, e.g. is at the WCDMA network 213, the packet is routed 404via the tunnel over the WCDMA network and the IP network to the homeagent 216 and further to the external address. If the selected externalaccess is in the second mobile router 403, e.g. if it is at the GPRSnetwork 211, the data packet is forwarded or tunneled 405 to the secondmobile router 207. In the second mobile router, external access isselected 406 according to the same data as for the selection done in thefirst mobile router, such that the same external access is selected,i.e. the GPRS network access 211. Then the packet is routed 407 to thehome agent via the tunnel over the GPRS network and the IP network.

The step of selecting external access also comprises reading theinformation in the data packet to detect whether the data packet belongsto an already recorded flow. This detection takes place by e.g.comparing the flow ID of the data packet to flow IDs stored in adatabase in the mobile router. If the data packet belongs to an alreadyrecorded flow, the selection will be done according to a routingdecision made for a previous packet of the already recorded flow. Forthis reason, the access selection for the previous packet was recordedand stored in the mobile router as a flow state comprising flowidentification and routing decision.

If the packet belongs to a previously unidentified flow the MR will inaddition to using external access information, select access based onaccess selection policies configured in the MRs. Such policies may, forexample, have been pre-configured by the MR operator or the MNN user,such as subscription profiles, access classifications and selectionprinciples, Other policies will change dynamically, such as load-sharingalgorithms etc. An access selection policy may also be of the type:

-   -   To aggregate the throughput of the different accesses to improve        the access throughput experienced by the MNNs.    -   To apply load-sharing policies to make the most efficient use of        the available access resources (e.g. to maximize the end-user        experience).    -   To differentiate MNNs e.g. based on subscription profiles.    -   To differentiate flows e.g. based on application.    -   To provide redundancy, e.g. using one of the available accesses        as a backup that is activated only when the other        access/accesses is/are broken.

For all MRs to make the same decision given the same input, the accessselection policies are also synchronized between the MRs, when required,for example when a policy has changed.

As mentioned above, for a packet belonging to a previously unidentifiedflow, the MR will create and store a state for the flow, which statecomprises the routing decision and a flow identification. According toan alternative embodiment of the invention, the flow state can also betransmitted to other mobile routers such that the flow state issynchronized between the MRs. Thereby, it will be assured that the MRswill make the same routing decision even if packets are received atdifferent MRs.

An access selection policy may either be statically configured by e.g.the operator, regarding for example how and if load sharing is to beused and which access selection principles that shall be used, or thepolicy may be dynamically configured, regarding for example the loadsharing and access selection principles that are going to be used forthe moment. Any user preferences may also be used in a policy. Thepolicies may also include data of more dynamic nature, such assubscription profiles. An example of a selection principle could e.g. bethat a certain application, indicated by a certain port number, shouldbe sent over the available access link that has the highest bandwidth.Another example is that a certain real-time application, indicated by acertain port number, should be sent over the available access link thathas the lowest latency. An example of an access classification could bethat a satellite access is classified as a high latency access. Anotherexample could be that an IEEE 802.11a access (W-LAN) is classified as ahigh bandwidth access. An example of a simple load sharing algorithm isto allocate flows to different accesses according to round robinprinciples. However, once an access has been selected for a certainflow, the same access should preferably be kept for the entire lifetimeof the session/flow. Another example of a load sharing algorithm is tostrive to maintain an equivalent relative saturation of the availablebandwidth of the respective available accesses. An example ofinformation that could be included in a subscription profile could bethat a concerned subscriber is allowed to use only low and mediumbandwidth access like e.g. GPRS and WCDMA, whereas higher bandwidthaccess like IEEE 802.11a may be used for the concerned subscriber onlyif no accesses with lower bandwidth are available.

FIG. 5 shows another exemplary communication system wherein the presentinvention can be used. In this example, the moving network is a PersonalArea Network (PAN). A PAN is a network that wirelessly connectscommunication devices being in the vicinity of a user into a short-rangecommunication network. The PAN is then constituted by the communicationdevices that are within short-range communication distance of eachother. The PAN can for instance comprise the communication devices thatthe user is carrying with him/her or the network within the user'spersonal car. The PAN consists of a switched Ethernet network based onfor instance Bluetooth running the PAN profile. Some of the PAN deviceshave external access facilities. As described in co-pending patentapplication PCT/SE2004/001027 by the same applicant, the external accessfacilities of these PAN devices can be used by all devices in the PAN toget external access. Thereby, the PAN devices having external accessfacilities function as mobile routers for the PAN.

The PAN 501 according to FIG. 5 comprises PAN devices 502-505, fromwhich the two PAN devices 504, 505 have external access possibilitiesand, consequently, act as mobile routers (MRs) for external networkaccess. The MRs 504, 505 are also responsible for mobility management ofthe moving network, i.e. the PAN. The external accesses provided by theMRs can for instance be a cellular phone 504 providing WCDMA access 511and a PDA 505 providing WLAN access 512. These accesses can according tothe invention be available at the same time and the solutions/mechanismsdescribed in this application look into the cases where the PAN hasseveral MRs providing one or several external access each. As in the VANwith multiple MRs shown in FIG. 3, in this example, the MRs in the PANshare the same Home Agent 516 and the same prefix from the address rangeof their home network 515. The MRs are communicating with the Home Agent(HA) deployed in the home network via tunnels setup to the home agentfor each available external access. The example in FIG. 5 shows twotunnels from the PAN to the home agent.

The main advantages achieved by having support for simultaneousmulti-access for PANs are:

-   -   Being able to move traffic between accesses (and MRs) when links        go up and down when for instance the user moves out of coverage        for WLAN. This case can also occur if one of the MRs        ‘disappears’ from the PAN, e.g. moves out of Bluetooth coverage        or simply is switched off.    -   That a user of the PAN can select which access and MR to use and        change the selection, e.g. if the user for some reason wishes to        change access and move the traffic from one access to another        (which may also mean moving the traffic from one MR to another).        The reasons for the user to change MR may be, e.g.,        cost-reasons, corporate policy reasons etc.    -   That a greater accumulated bandwidth can be provided for        external network access for the PAN, since traffic can use        different accesses, i.e. some traffic can use for instance the        cellular access and other traffic can use the WLAN traffic.

The solutions according to the invention would function in a similar wayfor this communication system comprising the PAN as for thecommunication system comprising a VAN shown in FIG. 3.

In the solutions according to the invention, an overall goal is to makethe data packet routing work in a seamless manner across multiple MRs.As mentioned above, an important aspect for this to work is that atleast some data is synchronized and coordinated between the MRs in amoving network. Such data may be information regarding the externalaccesses of all mobile routers in the moving network, such as types andproperties of available accesses and states of the available accesses.Such data may also be access selection policies, i.e. policies how toroute data packets and managing flows comprising data packets. It mayalso comprise which MR that is responsible for sending explicitinstructions to a Home Agent regarding how the home agent should routepackets in the opposite direction (from HA to MNN). Therefore, thesolutions according to the invention provides a mechanism to ensure thata data packet belonging to a flow from an MNN is routed through the MRthat is connected to the access selected for that particular flow.

The invention comprises solutions according to two different principles:a distributed solution and a centralized solution.

In the distributed solution all MRs have equal status and operateaccording to the same principles using the same mechanisms. All MRs havethe same information used for access selection. Thereby, they will makethe same decisions and select the same access for a specific packet.

In the centralized solution, one of the MRs takes on a superior rolecalled super Mobile Router (super MR). The super MR is responsible forall flow management related decisions in the moving network, e.g., perflow access selections. In both solutions, the tunnel establishmentmechanisms functions as mentioned above and as shown in co-pendingapplication PCT/SE2004/001578. Also, the mechanisms to convey explicitflow management instructions to the HA, functions as shown inPCT/SE2004/001578.

Basic Principles of the Distributed Solution

In FIG. 6 it is shown how routing of a packet functions according to theembodiment of the invention called the distributed solution. In thedistributed solution all MRs are “equal” and perform their ownindividual actions and decisions. For instance, all MRs may announcethemselves as default gateways to the MNNs. As a consequence, MNNs maysend packets belonging to data flows to any of the MRs. Therefore theMRs must be synchronized in terms of routing decisions and the data thatthe decisions are based on.

In FIG. 6, each MNN 601, 602, 603 selects a default router arbitrarily,(illustrated by the broad arrows from the MNNs to MR1 or MR2). For anuplink flow, the data packets are routed the following way (see theblack narrow arrow in the figure): From an MNN 602 the packet is sente.g. to MR2 604, since in this case the MNN has selected MR2 604 as itsdefault router. The MR2 makes, according to this example, a routingdecision that external Access 4 606 is the best access, and MR2 forwardsthe packet to MR3 605 that provides that access. The MR3 will, accordingto an embodiment of the invention, also make a routing decision, whichis based on exactly the same input parameters, and will consequentlyalso find that this packet should be sent over the Access 4 606 to ahome agent 607 of the MR3 605. For a downlink flow, a packet will besent over the Access 4 606 from the home agent 607 to the MR3 605. MR3will deliver the packet directly to MNN 602.

Basic Principles of the Centralized Solution

In FIG. 7 it is shown how routing of a packet functions according to anembodiment of the invention called the centralized solution. In thecentralized solution one of the MRs takes on a superior role calledsuper MR. The super MR is selected (and re-selected when needed) amongthe available MRs using a distributed super MR selection mechanism,which will be described further down in the application. The super MR isthe only MR that is visible to the MNNs, i.e. only the super MRadvertises itself. Thus, all the MNNs set their default route towardsthe super MR and send their data flows to it. The super MR makes all theaccess selection decisions and forwards or redirects flows to the otherMRs when needed. To enable the super MR to make appropriate per flowaccess selections all the other MRs must send all their MR specificinput data to be used in the access selection process to the super MR.

In FIG. 7, all MNNs 701, 702, 703 have the selected super MR, which inthis example is MR2 704 as their default router (illustrated by thebroad arrows from the MNNs to the MR2). Thereby, all data originatingfrom an MNN and destined to an external address ends up at MR2 704. Froman MNN 702 a packet is sent to MR2 704. The MR2 makes, according to thisexample, a routing decision that external Access 4 706 is the bestaccess, and MR2 forwards the packet to MR3 705 that provides thataccess. The MR3 will, according to an embodiment of the invention, alsomake a routing decision, which is based on exactly the same inputparameters, even though it is not the super MR, and it will also findthat this packet should go over the Access 4 706 to a home agent 707 ofthe MR3 705. For a downlink flow, a packet will be sent over the Access4 706 from the home agent 707 to the MR3 705. MR3 will deliver thepacket directly to MNN 702.

Synchronization of Input Data for Access Selection in the DistributedSolution

To ensure that multiple MRs in a moving network make consistent per flowrouting decisions, the data that these decisions are based on should besynchronized between the MRs. The data that may be used as input datafor routing decisions (in addition to the parameters characterizing theflow itself, such as addresses and ports), and which consequently haveto be synchronized among the MRs, include access selection policies, themoving network nodes' end user/device profiles, types and properties ofthe available access links, the current load on the available links,load sharing algorithms and policies, etc.

Some of this data is highly dynamic, such as the current load on theavailable links, whereas other data changes less frequently, e.g. thetypes and properties of the available links.

Attributes describing this input data may be stored in ManagementInformation Base (MIB) attributes and be transferred between the MRsusing Simple Network Management Protocol (SNMP). Another way todistribute the data among MRs in a PAN would be to use the PANManagement Protocol (PMP) described in the pending patent applicationPCT/SE2004/001027. Yet a feasible way would be to use a protocoldedicated for this purpose. In the distributed solution, a dedicatedprotocol should preferably use a multicast address to distribute dataamong the MRs.

Synchronization of Input Data for Access Selection in the CentralizedSolution

In the centralized solution the super MR will be first to make flowrouting decisions, as all MNNs will send their packets to it. However,there is a need for all MRs in the moving network to receive somerouting decision data, such as existing mobile routers and externalaccesses in the moving network, as:

1. The super MR role may change; 2. The super MR will forward flows toother MRs depending on the selected access and each of these MRs need tomake the same decision; 3. The dynamic data (such as current load on theavailable links) must be distributed to at least the super MR, and 4.Any MR may need to send explicit routing instructions to the HA for thedownlink part of a flow, i.e. the flow from a HA to an MNN via any ofthe MRs.

Therefore, according to one embodiment of invention, the solution forsynchronizing input data for access selection in the centralisedsolution is mainly the same as in the distributed solution describedabove, i.e. that substantially all data that routing decisions are basedupon are synchronized between the mobile routers in the moving network.

Although, according to another embodiment of the centralized solution,routing decision data is not synchronized at the mobile routers that arenot selected as the Super Mobile router. In this case, in the scenariodescribed in FIG. 7, the MR3 705 would not take any routing decision andselect external access. Instead, the super MR, MR2 704 in FIG. 7, wouldinform about the access that it has selected, for example by marking thepacket to be routed in a special manner indicating the routing decision,by tunneling the packet in a certain manner or by sending an explicitinstruction comprising the routing decision, for example by sending aflow state, when such a state has been recorded.

According to yet another embodiment of the centralized solution, onlysome routing decision data regarding access status and policies issynchronized at the mobile routers that are not selected as the superMR, e.g. MR3 in FIG. 7. The routing decision data that is synchronizedwould be enough data to be able to make a correct routing decision whenthe MR, e.g. the MR3 in FIG. 7, receives a packet from a super MR. Thiswould be possible in the centralised solution because this MR, e.g. MR3in FIG. 7, would know that it will only make a routing decision betweenits own external accesses, and that it shall never send the packet toanother mobile router.

If data used for access selection is sent only to the super MR, then nomulticast group is needed for this data distribution, unicast deliveryto the super MR suffices.

Routing a Flow Through the Mobile Router of a Selected Access

The procedure described in the co-pending patent applicationPCT/SE2004/001578 is defined for a moving network with a single MR, butthe routing decisions are basically made in the same way for multipleMRs. In addition, each MR will have some additional input data, such asexternal accesses available behind other MRs, to base its decisions on.The routing action is extended, as not all outgoing accesses are localto the MR, but are reachable through another MR. Finally, further downin the application, ways are defined to ensure that no routing loops orredirection loops are formed between the MRs.

For a particular flow, the MR that receives a packet may or may not bethe correct outgoing MR, depending on the routing decision. For outgoingpackets, i.e. in the direction from an MNN to the HA, if another MR isthe outgoing MR, i.e. has the correct external access for this flow, theMR that received the packet will forward the packet towards the outgoingMR. Tunneling from the MR that received the packet to the outgoing MR isan alternative to forwarding, but the effect is exactly the same. For anincoming packet from the HA, the MR simply delivers it to thedestination MNN.

Any MR that receives a packet classifies what flow it belongs to andfollows earlier routing decisions, if there are any, such that the sameaccess is selected as for previous packets of the flow. If the packetbelongs to a previously (by this MR) unidentified flow, the MR will makea routing decision, select what access or accesses to use, both for theuplink and downlink parts of the flow. In the case when the downlink anduplink parts of the flow are asymmetrical, the uplink and downlink partsof the flow may use different accesses, which accesses may even belongto different MRs. This routing decision will be stored such that it canbe used for subsequent packets of the same flow. The access/accessesselected indirectly points out what outgoing MR should be used foruplink packets and what care-of address should be used for downlinkpackets.

If the access selected for the downlink part of a flow is different fromaccess selected for the uplink part of the same flow, one of the MRsshould send explicit instructions to the HA, in substantially the samemanner as explained in PCT/SE2004/001578. Unless the downlink tunnelselection for a particular newly identified (asymmetric) flow is alreadycovered by previously sent instructions to the HA, it is preferred thatthe outgoing MR sends this instruction to the HA. This means that onlyone MR will send the instruction, which is important not to confuse theHA. The MR that sends the instruction has to be one involved in thecurrent routing path of the flow. The MR that has the desired downlinkaccess may not be in the routing path until the HA has been instructed,which means that this MR will not see any packets and will not performany routing decisions. The MRs that are in the current routing path are:

1. the MR that MNN uses as default router;2. the outgoing MR, and3. the receiving MR for the downlink part of the flow, which may be thedefault MR for unidentified flows from the home agent's point of view.

Sending Explicit Instructions to the HA

As described in above, an MR may send explicit tunnel selectioninstructions to the HA triggered by a new flow. In that case theexplicit tunnel selection instructions would pertain only to thatparticular flow. In this case the MR that identifies the outgoing flowand that is the outgoing MR should be the one sending the explicitinstructions to the HA.

However, MRs may also send more generic explicit tunnel selectioninstructions, covering e.g. types of flows, which the HA will use forflows to come. The mechanisms for this are described inPCT/SE2004/001578 for the single MR solution. In this multiple MR case,any MR could potentially send the instructions. One possible approachfor this case would be to let each MR be responsible for sending theinstructions that point towards a tunnel that leads to the MR itself.Another approach, useful particularly for the centralized solution,would be to let an MR send instructions related to all tunnels. Forinstance, in the centralized solution the super MR could be responsiblefor sending all explicit instructions to the HA. The super MR could dothis even for the instructions that pertain only to a single flow andthat are triggered by a new outgoing flow, since all outgoing flows aretunneled through the super MR.

When MRs are allowed to send explicit tunnel selection instructionspointing towards tunnels that do not lead to the MR itself, aconsequence is that the care-of addresses of the MRs have to be includedin the information that is distributed among the MRs. The reason is thatin the explicit instructions sent to the HA, the tunnel to be selectedis indicated by the address of a tunnel endpoint at the MR and thistunnel endpoint address is the care-of address of the MR.

Super MR Selection

In the embodiments of the invention where the centralized solution isused, the MRs in the moving network have to agree on which of the MRsthat should act as the super MR. This super MR selection process shouldbe seen as a dynamic, continuously ongoing process, since new MRs mayappear, as new accesses become available, and old MRs may cease to beMRs, if their accesses become unavailable, or even disappear, when theyare disconnected from or moved out of radio range of the moving network.

The proposed super MR selection process is based on the MRs exchangingtheir respective so-called Super MR Selection Number (SMSN), which is anumber in the range [SMSNmin . . . SMSNmax], along with the IP address.The MR that has the greatest SMSN is selected as the super MR. If morethan one MR has the same greatest SMSN, then the one of those MRs thathas the greatest IP address is selected as the super MR. As soon as anode turns into an MR, i.e. when a node in a moving network offers othernodes in the moving network access to an external network via itself,e.g. through a newly appearing access link, it should generate an SMSNand join the super MR selection process by starting to exchange SMSN andIP address with the other MRs, if any, in the moving network. The MRshould not advertise itself as a router to the moving network nodes,i.e. send Router Advertisement messages, in the moving network, unlessit has determined, through the super MR selection process, that it isthe super MR of the moving network.

An MR can generate its SMSN values in three different ways, asillustrated in FIG. 8:

1. Randomly generate the SMSN in the default range 801[SMSNdefault_range_min . . . SMSNdefault_range_max], whereSMSNdefault_range_min>SMSNmin andSMSNdefault_range_min<SMSNdefault_range_max<SMSNmax.

2. Randomly generate the SMSN in a configured range 802[SMSNconfigured_range_min . . . SMSNconfigured_range_max], whereSMSNconfigured_range_min>SMSNmin andSMSNconfigured_range_min≦SMSNconfigured_range_max≦SMSNmax.SMSNconfigured_range_min=SMSNconfigured_range_max indicates that the MRis configured to set itsSMSN=SMSNconfigured_range_min=SMSNconfigured_range_max.3. Set the SMSN=SMSNmin. This SMSN value is used only by a node thatceases to be a MR, e.g. because its external access becomes unavailable.

An administrator of the MRs may utilize the SMSN configurationpossibilities to control or bias the super MR selection process in amoving network. For example, the administrator could configure the MRsto randomly generate the SMSN in different sub-ranges, or even configurethe MRs to set the SMSN to different specific values, depending on thetype or properties of their available access(es). Typically, a highcapacity access would result in a higher SMSN sub-range or value beingused than a low capacity access. In general, a beneficial way of usingthe SMSN configuration possibilities would be to match the SMSNconfigurations with the routing policies/flow management policies, suchthat the MR that, under the current circumstances, is expected to routethe most traffic through its access(es), is also selected as the superMR.

A list of events that may trigger generation of a new SMSN in a nodecomprises:

-   -   The node becomes an MR;    -   The node ceases to be an MR, in which case the node sets its        SMSN=SMSNmin;    -   The properties of the MR and/or its accesses, change in a way        that affects the range within which the mobile router's SMSN        should be generated, e.g. switching from the default range to a        configured range or vice versa, or switching from one configured        range to another. An example of such a property change may be        that a new access type becomes available or unavailable. Another        example may be that the node becomes the super MR;    -   The mobile router's SMSN configuration is changed in a way that        affects the range within which the mobile router's SMSN should        be generated, e.g. switching from the default range to a        configured range or vice versa, or switching from one configured        range to another.

For the super MR selection process, a novel specific Super MR SelectionProtocol (SMSP) may be defined including a single message type, e.g.denoted “SMSN Announcement”. An SMSN Announcement includes at least theSMSN of the sending node. The receiver of an SMSN Announcement alsoneeds the IP address of the sending node to associate with the receivedSMSN. This IP address can be included in the SMSN Announcement or thereceiver may extract it from the IP header. If the moving network e.g.is a PAN, the PAN Management Protocol defined in PCT/SE2004/001027 maybe used in the Super MR Selection process.

SMSP is preferably an application level protocol running on top of UDP.The SMSN Announcements are preferably multicast to a multicast addressdedicated for MRs, but broadcasting the messages would also work.

Each MR should periodically send SMSN Announcements. The time intervalbetween two SMSN announcements should be SMSNbase_period+Drand, whereSMSNbase_period is a fixed value and Drand is a random delay value thatis randomly generated for each SMSN Announcement period. Drand isgenerated within the interval [Drand_min . . . Drand_max]. Thus themaximum time between two SMSN Announcements transmitted from the same MRis ideally SMSNideal_max_period=SMSNbase_period+Drand_max. However, in ashared medium network the actual transmission of a SMSN Announcement maybe further delayed due to contention for the shared medium (e.g.collisions).

When joining the super MR selection process a node should wait for atleast N SMSNideal_max_periods before selecting a super MR, i.e. beforedetermining which MR it should consider to be the super MR. Anappropriate value of N could be e.g. N=2.5. Likewise, a nodeparticipating in the super MR selection process should not consider thesuper MR, or any other MR, as unavailable until at least NSMSNideal_max_periods have passed without receiving an SMSN Announcementfrom the super MR or other MR. When the node determines that the superMR is unavailable, it selects the one of the remaining MRs that hasannounced the greatest SMSN, or, if several MRs has announced the samegreatest SMSN, the one of these that has the greatest IP address.

However, when a node participating in the super MR selection processreceives an SMSN Announcement from another MR than the current super MR,including an SMSN that is greater than that of the current super MR, orif the node itself sends such a SMSN Announcement, then the node shouldimmediately determine that the MR sending the concerned SMSNAnnouncement is the new super MR. Likewise, if a node participating inthe super MR selection process receives an SMSN Announcement from thecurrent super MR containing a new SMSN value that is no longer greatenough to motivate the sending node's status as the super MR, i.e. ifthe announced new SMSN is smaller than that of another MR or equal tothe SMSN of another MR that has a greater IP address, then the nodeshould immediately select a new super MR based on SMSN Announcementsreceived from the other MRs.

When an MR (the super MR or another MR) ceases to be an MR, it shouldset its SMSN=SMSNmin and keep sending at least M more SMSN Announcementswith the SMSN=SMSNmin, in order to clearly notify the other MRs that itis no longer a MR, before leaving the super MR selection process. Anappropriate value of M could be, e.g., M=2.

Due to long timeouts of the default router configuration in the nodes inthe moving network, it may take a significant time before a super MRchange is reflected in the way the nodes of the moving network directtheir outgoing external traffic, i.e. to which router they send packetsbound for destinations outside the moving network. Therefore, a methodenforcing conservative super MR changes may be useful. For instance, ifa certain external access frequently comes and goes, i.e. switchesbetween being and not being available, it may be beneficial that thesuper MR does not change every time the access comes or goes, even ifthe SMSN configuration of the affected MR, and the SMSN situation in themoving network as a whole, is such that a change in the availability ofthe external access would imply a super MR change.

There are different possible approaches for a method to enforceconservative MR changes:

-   -   Time based approach: An MR whose SMSN is to be changed due to a        changed property, e.g. that one of its accesses became available        or unavailable, delays the execution of this SMSN change. This        gives the changed property some time to change back again, in        which case the SMSN change is cancelled. This way SMSN        fluctuations, and consequently the frequency of super MR        switches, can be reduced. It should be configurable which type        of SMSN changes that should be delayed and which that should not        be delayed, e.g. that increases are delayed but not decreases,        or that the delay is triggered by certain property changes but        not by others.    -   Based on SMSN manipulations. When an MR becomes the super MR it        increases its SMSN to a higher value in order to reduce the risk        that it is quickly deposed from the super MR throne by another        MR that whose SMSN is increased. The super MR would keep the        high SMSN value until an SMSN change is triggered by any of the        usual triggering events, e.g. property changes, or until another        MR takes over the super MR role. The following are two concrete        proposals for how to implement this method:    -   When an MR that has generated its SMSN in the default range        becomes the super MR, i.e. when it determines itself to be the        super MR, it sets its SMSN=SMSNdefault_range_max+1 and can thus        only be replaced by an MR that has been configured to generate a        SMSN value greater than SMSNdefault_range_max.    -   When an MR becomes the super MR, i.e. when it determines itself        to be the super MR, it sets its SMSN=SMSNmax. Then, unless        another MR with a greater IP address sets its SMSN=SMSNmax,        which can only happen if the MR is configured to be able to do        so, the selected super MR will continue to be the super MR until        it ceases to be an MR or until its properties, or the properties        of its access/accesses, change in a way that according to its        SMSN configuration indicates that a new SMSN should be generated        in the node despite its status as the super MR.    -   A combination of time based methods and methods based on SMSN        manipulations.

A possible variation of the super MR selection scheme, is to let a nodeinclude in its SMSN Announcements, in a field denoted “super MR addressfield”, the IP address of the MR that it currently considers to be thesuper MR. When this variation/option is used, an MR would not forwardtraffic to a selected super MR, until the selected super MR announcesthat it considers itself to be the super MR, by including its own IPaddress in the super MR address field of its SMSN Announcement. Thisfeature could be used to avoid loops, if inconsistencies occur. An MRthat currently does not know which MR it considers to be the super MRindicates this by including an all-zero address in the super MR addressfield of its SMSN Announcements or by omitting the super MR addressfield.

Redirection Mechanism

If the MR that receives an outgoing packet from an MNN, e.g. the firstMR, makes a routing decision and finds that another MR will be theoutgoing MR, it may send a redirect message back to the MNN to instructthe MNN that for subsequent transmission of packets to the particulardestination, the MNN should use a different next hop towards the otherMR. The next hop is the link-local IPv6 address of the outgoing MR. Thiswill reduce the number of hops by one as subsequent packets will be sentdirectly to the outgoing MR and not via the first MR. The redirectmessage may be an Internet Control Message Protocol (ICMPv6) for theInternet Protocol Version 6 (IPv6) Redirect message, which is describedin “Internet Control Message Protocol (ICMPv6) for the Internet ProtocolVersion 6 (IPv6)”, by A. Conta et al., published on the Internet as RFC2463 in December 1998.

Conceptually, the redirection is stored (with a limited lifetime) in adestination cache of the MNN.

If the ICMPv6 Redirect message is used, this redirect is valid for theparticular destination IPv6 address. This does not exactly match thegranularity of flow differentiation that this invention aims at, sincean MNN may very well have multiple flows towards a single destination.In this case the MRs must be able to route these flows independentlyover different accesses. The solution to this is to extend the standardfor the redirect message to optionally also include source port number,destination port number, protocol, flow label or Security ParameterIndex (SPI). Although, this would require changes to the MNNs.

Routing and Redirection Loop Avoidance

If the different mobile routers make inconsistent routing decisions,i.e. if they, for some reason would select different external accesseseven though they should base their selection on the same information,there is a risk that routing loops are formed within the moving networksuch that MRs forward a certain outgoing packet back and forth betweeneach other without the packet exiting through en external access. Oneway to cope with routing loops is for an MR to detect when an outgoingpacket that, according to the routing decision of the MR, should be sentthrough an access of another MR is received from an MR (instead of froman MNN). When such a packet is detected the MR overrides its regularrouting decision and sends the packet through one of its own accessesinstead of forwarding it to another MR. This behavior avoids that arouting loop is caused by inconsistent routing decisions. The MR coulddo so with the underlying assumption that the regular distribution andsynchronization of access selection related information will eventuallyresolve the inconsistency.

When an MR sends a redirect message to an MNN, as described above, theMR records, and maintains for a short while, maybe one or a couple ofseconds, the flow state for the redirected packet. If, for some reason,the MR receives from the MNN, a subsequent packet belonging to theredirected flow, the MR concludes that a redirection loop has beenformed. In that case, the MR does not send another redirect message tothe MNN, but overrides its regular routing decision and sends the packetthrough one of its own external accesses. Thereby, a redirection loop isavoided. The MR could do so with the underlying assumption that theregular distribution and synchronization of access selection relatedinformation will eventually resolve the inconsistency.

For both routing loops and redirection loops, the MR may also use a moreproactive approach. Instead of waiting for the regular distribution ofaccess selection related information to resolve the inconsistency, theMR may, immediately after detecting a routing or redirection loop,distribute its own relevant data and indicate in a message comprisingthe access selection related information that inconsistencies arepresent. This indication will trigger immediate sharing of all relevantinformation among the MRs.

FIG. 9 shows a mobile router 900 according to an embodiment of thepresent invention, for example the mobile router MR1 in FIG. 3. Themobile router 900 comprises:

-   -   An internal interface 901, for receiving data packets and        information from MNNs and other MRs in the moving network and        for sending packets and information to MNNs and other MRs in the        network;    -   A processor 902 for selecting external access for routing data        packets based on information in the data packets and other        information relevant for external access selection, such as        information about the external accesses in the network and        access selection policies, wherein the processor is arranged to        analyse the information in the data packets and other relevant        information and to make a routing decision based on the analyses        such that external access is selected;    -   A memory 905 for storing information about external accesses in        the network, access selection policies and flow states regarding        routing decisions for previously routed packets, and,    -   At least one external interface, in this example a first        external interface 903 and a second external interface 904, for        getting access to at least one external access such that data        can be routed via a tunnel set up through the at least one        external access to the home agent.

Corresponding means for performing the steps according to claims 1-16may be implemented with computer program software in a mobile router.

Compared to conventional moving network procedures, the proceduresdescribed in previous co-pending patent application PCT/SE2004/001578allowed a single MR to have multiple active tunnels to increasethroughput, provide better redundancy and to be able toload-balance/share the traffic, without downgrading e.g. transport layercharacteristics such as TCP measurements by making arbitrary forwardingdecisions over different paths per flow. The procedures described inPCT/SE2004/001578 also allowed the moving network to differentiatetraffic to and from different MNNs over different accesses. It alsoallowed the moving network to differentiate flows over differentaccesses, such that flows of a particular type may be forwarded over aparticular access, for instance. Further, the procedures described inPCT/SE2004/001578 allowed a single MR to make all decisions on over whataccess each particular flow is routed. The HA will follow the mobilerouter's decisions. The mobile router's decisions will be transparent tothe MNNs and they will not have to worry about multiple accesses thatare available to the moving network, while still being able to use them.

The present invention as described above has all the advantages of theprocedures described in the previous patent application. In addition,this invention further enhances the procedures described in the previouspatent application by the possibility to use multiple MRs in a movingnetwork while still honoring the requirements and advantages of theprocedures described in the previous patent application. Each MR mayprovide one or multiple external accesses and the union of all accesseson all MRs are made available for use by the MNNs in the moving network.The result towards the MNNs is the same as in the single-MR case. Thismeans that the MRs all behave consistently and according to the samepolicy. The result, i.e. the access selection, is the same independentlyof the default router selected by an MNN.

In both the distributed solution embodiment and the centralized solutionembodiment of the present invention, the MRs can back up for each other.The failure of an MR only means that the moving network loses theaccesses provided by that MR; it does not mean that the moving networkloses all connectivity to the infrastructure. This invention does notplace any additional requirements on the MNNs, except if the optionalenhanced redirection mechanism is to be used. This invention does notplace any additional requirements on the Home Agent other than thoserequired by the previous procedures.

In the drawings and specification, there have been disclosed preferredembodiments and examples of the invention and, although specific termsare employed, they are used in a generic and descriptive sense only andnot for the purpose of limitation, the scope of the invention being setforth in the following claims.

1.-32. (canceled)
 33. A method in a communication system for routing adata packet originating from a moving network node in a moving networkvia a first mobile router of the moving network to a home agent in ahome network of the moving network, wherein the first mobile router hasthe ability to access at least one first external access through whichat least one first external access one tunnel each is set up to a firsthome agent of the first mobile router and wherein the moving network hasat least one second mobile router, and wherein the at least one secondmobile router has ability to access at least one second external access,through which at least one second external access one tunnel each is setup to a second home agent of the at least one second mobile router, andwherein each mobile router in the moving network has informationregarding the at least one first and the at least one second externalaccesses in the moving network, the method comprising the steps of:receiving, at the first mobile router, a data packet from a movingnetwork node; selecting, in the first mobile router, one of the at leastone first or second external accesses for routing the data packet to thefirst or second home agent based on information in the data packet andon the information regarding the at least one first and the at least onesecond external accesses; and routing the data packet from the firstmobile router to the first or second home agent via the tunnel set upthrough the selected external access.
 34. The method according to claim33 wherein the step of selecting is also based on access selectionpolicies stored in the first mobile router.
 35. The method according toclaim 33 or 34, wherein the method further comprises the step of, whenrequired, exchanging the information regarding the at least one firstand the at least one second external accesses in the moving network,between the first and the at least one second mobile router in themoving network such that the information regarding the at least onefirst and the at least one second external accesses is synchronizedamong the first and the at least one second mobile router.
 36. Themethod according to claim 34, wherein the method further comprises, whenrequired, synchronizing the access selection policies between the firstand the at least one second mobile router in the moving network.
 37. Themethod according to claim 33 or 34, wherein the step of routing the datapacket from the first mobile router further comprises: routing the datapacket from the first mobile router to one of the at least one secondmobile router, if the selected external access is one of the at leastone second external access; and routing the data packet from the one ofthe at least one second mobile router to the second home agent via theselected external access.
 38. The method according to claim 37, furthercomprising, in the one of the at least one second mobile router afterthe data packet has been routed from the first mobile router to the oneof the at least one second mobile router, the steps of: selecting one ofthe at least one second external access for routing the data packet tothe second home agent based on information in the data packet and on theinformation about the external accesses in such a way that the sameexternal access is selected as was selected by the first mobile router;and routing the data packet from the one of the at least one secondmobile router to the second home agent via the selected external access.39. The method according to claim 33 or 34, wherein the step ofselecting further comprises: reading the information in the data packetto detect whether the data packet belongs to an already recorded dataflow; and, if the data packet belongs to an already recorded data flow,making a routing decision for the data packet according to a routingdecision stored in a flow state for the already recorded data flow andaccording to the information regarding the at least one first and the atleast one second external accesses in the moving network, and, if thedata packet belongs to a flow that has not been recorded: making arouting decision for the data packet according to access selectionpolicies and according to the information regarding the at least onefirst and the at least one second external accesses in the movingnetwork; recording a flow state for the flow that the data packetbelongs to, which flow state comprises the routing decision and a flowidentification.
 40. The method according to claim 33 or 34, wherein thefirst mobile router is a super mobile router, and wherein the supermobile router instructs the moving network nodes to send data packetsthat are directed to a node external of the moving network via the supermobile router.
 41. The method according to claim 40, wherein the firstmobile router is selected to be the super mobile router based on a supermobile router selection number (SMSN) for each of the first and the atleast one second mobile router, which SMSN is determined by each of thefirst mobile router and the at least one second mobile router andexchanged between the first mobile router and the at least one secondmobile router such that each mobile router is aware of each mobilerouter's SMSN.
 42. The method according to claim 41, wherein the SMSN isdynamically determined and wherein the role of being the super mobilerouter may change dynamically between the first mobile router and the atleast one second mobile router based on the SMSN and wherein a mobilerouter generates an SMSN if any of the following events occur: themobile router is a new mobile router appearing in the moving network;the mobile router ceases to be a mobile router in the moving network; aproperty of the mobile router and/or its external accesses changes; oran SMSN configuration of the mobile router changes.
 43. The methodaccording to claim 42, wherein each of the first and the at least onesecond mobile router selects the first mobile router as the super mobilerouter if the first mobile router has the highest SMSN, and wherein therole of the super mobile router is changed from the first to one of theat least one second mobile router if any of the following occurs: theSMSN of the first mobile router has been lower than the SMSN of one ofthe at least one second mobile router for at least a certain time; orthe SMSN of the first mobile router added with a certain value is lowerthan the SMSN of one of the at least one second mobile router.
 44. Themethod according to claim 33 or 34, wherein the first mobile router isany mobile router in the moving network.
 45. The method according toclaim 33 or 34 wherein a routing loop, being a packet is sent back andforth between two mobile routers due to inconsistent access selection,is avoided by the first mobile router: detecting whether the packet isreceived from one of the at least one second mobile router or from amoving network node, and, if the packet is received from one of the atleast one second mobile router, and sending the packet through one ofthe at least one first external access.
 46. The method according toclaim 33 or 34, wherein, if the selected external access is accessiblefrom one of the at least one second mobile router, the first mobilerouter sends a redirect message to the moving network node instructingthe moving network node to send the next data packet of the same flowdirectly to the one of the at least one second mobile router.
 47. Themethod according to claim 46, wherein, if the first mobile routerreceives a subsequent data packet belonging to the same flow as the datapacket for which the first mobile router sent the redirect message, thefirst mobile router sends the subsequent data packet through one of itsat least one first external access.
 48. The method according to claim 33or 34, wherein the first home agent is the same home agent in the samehome network as the second home agent.
 49. A mobile router of a movingnetwork in a communication system arranged for routing a data packetoriginating from a moving network node in the moving network to a homeagent in a home network of the moving network, wherein the mobile routerhas ability to access at least one first external access, through whichat least one first external access one tunnel each is set up to a firsthome agent of the mobile router, the mobile router comprising: means forstoring information regarding the at least one first external access andregarding at least one second external access, which at least one secondmobile router has the ability to access, and through which at least onesecond external access one tunnel each is set up to a second home agentof the at least one second mobile router; means for receiving a datapacket from a moving network node; means for selecting one of the atleast one first or second external accesses for routing the data packetto the first or second home agent, wherein the selection that the meansfor selecting is arranged to accomplish is based on information in thedata packet and on the information regarding the at least one firstexternal access and the at least one second external access; and meansfor routing the data packet to the first or second home agent via thetunnel set up through the selected external access.
 50. The mobilerouter according to claim 49, wherein the selection that the means forselecting is arranged to accomplish is also based on access selectionpolicies stored in the means for storing information in the mobilerouter.
 51. The mobile router according to claim 49 or 50, wherein themobile router has means for sending and receiving the informationregarding the at least one first and the at least one second externalaccesses, to and from the at least one second mobile router such thatthe information regarding the at least one first and the at least onesecond external accesses is exchanged and synchronized at the mobilerouter.
 52. The mobile router according to claim 50, wherein the mobilerouter further has means for synchronizing the access selection policieswith the at least one second mobile router in the moving network. 53.The mobile router according to claim 49 or 50, wherein the means forrouting the data packet is arranged for routing the data packet to oneof the at least one second mobile router, if the selected externalaccess is one of the at least one second external access.
 54. The mobilerouter according to claim 49 or 50, wherein the means for routing thedata packet is arranged for routing the data packet to the first homeagent via the tunnel set up through one of the at least one firstexternal access, if the selected external access is one of the at leastone first external access.
 55. The mobile router according to claim 49or 50, wherein the means for selecting is further arranged for readingthe information in the data packet to detect whether the data packetbelongs to an already recorded data flow; and, if the data packetbelongs to an already recorded data flow, making a routing decision forthe data packet according to a routing decision stored in a flow statefor the already recorded data flow and according to the informationregarding the at least one first and the at least one second externalaccesses in the moving network, and, if the data packet belongs to aflow that has not been recorded: making a routing decision for the datapacket according to access selection policies and according to theinformation regarding the at least one first and the at least one secondexternal accesses in the moving network; and recording a flow state forthe flow that the data packet belongs to, which flow state comprises therouting decision and a flow identification.
 56. The mobile routeraccording to claim 49 or 50, wherein the mobile router is a super mobilerouter, and wherein the super mobile router is arranged to instruct themoving network nodes to send data packets that are directed to a nodeexternal of the moving network via the super mobile router.
 57. Themobile router according to claim 56, wherein the mobile router wasselected to be the super mobile router based on a super mobile routerselection number (SMSN), determined for each of the mobile router andthe at least one second mobile router and exchanged between the mobilerouter and the at least one second mobile router.
 58. The mobile routeraccording to claim 57, wherein the SMSN is dynamically determined andwherein the mobile router is arranged to determine a new SMSN if any ofthe following events occur: the mobile router is a new mobile routerappearing in the moving network; the mobile router ceases to be a mobilerouter in the moving network; a property of the mobile router and/or itsexternal accesses changes; or an SMSN configuration of the mobile routerchanges.
 59. The mobile router according to claim 49 or 50, wherein themobile router is any mobile router in the moving network.
 60. The mobilerouter according to claim 49 or 50, wherein a routing loop, being apacket is sent back and forth between two mobile routers due toinconsistent access selection, is avoided by the mobile router beingarranged for detecting whether the packet is received from one of the atleast one second mobile router or from a moving network node, and, ifthe packet is received from one of the at least one second mobilerouter, sending the packet through one of the at least one firstexternal access.
 61. The mobile router according to claim 49 or 50,wherein, if the selected external access is accessible from one of theat least one second mobile router, the mobile router is arranged forsending a redirect message to the moving network node instructing themoving network node to send the next data packet of the same flowdirectly to the one of the at least one second mobile router.
 62. Themobile router according to claim 61, wherein, if the mobile routerreceives a subsequent data packet belonging to the same flow as the datapacket for which the mobile router sent the redirect message, the mobilerouter is arranged to send the subsequent data packet through one of itsat least one first external access.
 63. The mobile router according toclaim 49 or 50, wherein the first home agent is the same home agent inthe same home network as the second home agent.
 64. A computer programproduct loadable into a memory of a digital computer device residing inthe mobile router, wherein the computer program product comprisessoftware code portions for performing the method of claim 33 when thecomputer program product is run on a computer device.